1. Field of the Invention
The present invention relates generally to machine tools, and more specifically to a workpiece seat for the machining of bar-shaped workpieces by milling and turning.
2. Discussion of Related Art
Various types of machine tools have been developed for the machining of workpieces in a single chucking by drilling and milling, as well as turning. This operation provides several advantages. For example, it provides higher machining accuracy, higher throughput and reduced idle times because set-up operations become unnecessary. In general, two types of such machines have been in use. In the first, the workpieces are processed for the most part by turning. In the second, the workpieces are processed preferably by milling. This latter type is akin to milling machines.
The machine tool shown in FIG. 1 belongs to the latter type. It has a relatively broad movable column 1 in bottom trough 2. Horizontal slides 3 are mounted on the upper side of the column. Slide 4 is movable in these slides. The slide has rails 5 extending transversely to slides 3. Vertical spindle stock 6 is movable in a second horizontal coordinate axis along the rails by a motor (not shown). At the front side of the spindle stock, spindle head 7 is supported in such a way that it can be rotated about an axis parallel to the second coordinate axis. Work spindle 8 is located in the spindle head. A motor (not shown) drives the work spindle. Milling, drilling, or turning tools can be alternatively clamped into the work spindle either manually or by means of a tool exchanger.
Console 10 is movably guided in the vertical coordinate axis at the front wall of the movable column in vertical guides 9. The console, apart from clamping surface 11, carries workpiece seat 12 for bar-shaped workpieces at a location laterally offset from the workspace.
Workpiece seats of the type shown in FIG. 1 are known. They serve for retaining bar-shaped workpieces that are, for the most part, automatically inserted into rearward opening 13. This insertion may be accomplished, for example, by means of a bar loader and suitable clamping means (not shown).
In prior art workpiece seats, at the rearward end of the spindle a fixing means is provided by which the spindle is located in the housing for performing particular drilling and milling operations, for example. This fixing means has an arrangement of clamping discs which are fixed on the spindle so that they radially project and, alternatively, are fixed in a corresponding housing recess, and when needed, can be strongly pressed against each other by a hydraulic piston, for example. However, this known fixing means is structurally complicated and occupies such space that the workpiece seat is elongated. Another technical disadvantage of this fixing means is that the spindle is only fixed at its rear end in the housing. As a result, if workpiece bars of relatively large diameter, for example 100 mm or more, are to be milled or drilled at a relatively high cutting performance, the spindle can elastically twist. This is because of the transmission of forces caused by the processing of the workpiece from the projecting end of the machined workpiece to the clamping chuck into the spindle and then to the fixing means arranged at the end of the spindle into the housing. These contortions of the spindle ultimately lead to positioning errors of the workpiece when it is machined.